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    <title>Document</title>
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    <script>
        const p = new Promise((resolve, reject) => {

        
        //1. 创建对象
        const xhr = new XMLHttpRequest()
        //2. 初始化
        xhr.open('GET','https://api.apiopen.top/getJoke')
        //3.发送
        xhr.send()
        //4. 绑定事件 ，处理响应结果
        xhr.onreadystatechange = function(){
            //判断
            if(xhr.readyState === 4){
                if(xhr.status >= 200 && xhr.status < 300){
                    //表示成功
                    resolve(xhr.response);
                }else{
                    //如果失败
                    reject(shr.status);
                }
            }
        }
    })

    //指定回调
    p.then(function(value){
        console.log(value);
    }, function(reason){
        console.log(reason);
    })
    </script>
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